Various technical approaches for a variable compression ratio are known from the prior art. Using variable adjustable engine components, the following specific possibilities are described below:                connecting rod with variable length        piston with variable compression height, and        crankshaft with variable crank radius.        
All these technical measures are directed, among others, to realize a variable compression.
For a variation of the cinematically effective lengths of the engine, i.e. the connecting rod length, the compression height or the crank radius, both telescopic elements and eccentric bearings are known. In some approaches, the active principle, “use of engine power for adjustment” is applied. Here, the forces acting at the eccentric bearing or at a telescopic element are used for adjustment. On the one hand, adjustment to a desired position should be as fast as possible, but, on the other hand, without damage and significant generation of noise. Experimental studies have shown that an adjustment from one end position to the other, for example, of an eccentric in the small connecting rod eyelet, can be realized within one working cycle, however, the components are damaged when a mechanical end stop is reached. As a consequence, the adjustment process must be decelerated and thus extends over several working cycles, which may be referred to as a multi-cycle principle. This, in turn, requires a device that prevents an unintentional reverse adjustment, i.e. a freewheel, for which the freewheeling direction must be reversible. This switchable freewheel can be realized by a hydraulic system. The known systems for realizing such a switchable hydraulic freewheel have in common that two support chambers are provided, which can support the forces and moments and prevent undesired reverse adjustment. These support chambers can be designed as reciprocating pistons or rotary pistons. DE 10 2005 055 199 describes a length-variable connecting rod for realizing a variable compression, abbreviated as VCR. Switching the freewheeling direction is effected by alternately opening and closing two supporting cylinders, wherein a 3/2-way valve is used to control the outflowing oil flow. This will be explained in detail in the following Figures with reference to FIG. 1 which shows the hydraulic circuit diagram used in DE 10 2005 055 199. Further, reference is made to the content of this publication to illustrate the basic structure of a VCR mechanism.
A VCR system of such design has the following disadvantages:    a. during the adjustment, a large oil volume flow is required to fill the momentarily expanding support cylinder. In order to supply the comparatively large momentary volume flow, sufficiently large-sized supply bores are required in the crankpin of the crankshaft, as well as supply grooves in the connecting rod bearing. Specifically the grooves in the connecting rod bearing weaken the bearing load capacity. Conversely, this means that the adjustment rate must be strongly limited in order to still be able to reliably supply the expanding support cylinder even with a small supply line system.    b. Upstream of the non-return valve, the supply pressure of the connecting rod bearing prevails. During the filling of the expanding support cylinder, the oil volume flow flowing through the non-return valve causes a pressure drop across the non-return valve. The maximum value of the adjustment rate has to be limited such that the oil pressure downstream of the non-return valve in the support cylinder still remains above the vapor pressure of the oil in order to avoid cavitation. In structures realized, it has been found that this cavitation criterion is already effective at an earlier time than the pulse criterion, i.e. the mechanical destruction due to an excessive impact speed of the support cylinder at the mechanical end stop.    c. When the system is in its final position, an oil volume flow is still drawn from the supply system. This is the case, for instance, if the left support piston shown in FIG. 1 has reached its lower end position. Then oil continues to flow from the supply system through the non-return valve into the left support cylinder and from there into the crankcase via the 3/2-way valve.
It is an object of the present invention to enable a faster switching and to thereby reduce an influence on the oil management of the engine.